Control systems or industrial controllers are used for controlling industrial processes such as machines, manufacturing equipment, and other factory automation apparatus. Industrial controllers receive various analog and/or digital process variables or other inputs representative of the status of a controlled process and generate outputs according to a control program or routine to control the process to one or more desired setpoints or other system performance criteria. Industrial control systems are typically comprised of two or more component modules performing various functions, such as I/O modules interfacing with field devices for sending and receiving outputs and inputs, control modules that run the control program and communicate with I/O modules, etc. Inputs from the controlled process and outputs transmitted to the process, whether analog and/or digital, pass through one or more I/O modules serving as an electrical interface between the controller and the controlled process, with the control system modules typically being located in one or more interconnected racks with backplanes and/or cabling providing a common communication link or network for data transfer between modules.
Certain industrial control applications require control of one or more actions on moving systems, such as pallets moving through a series of assembly stations (also called cells or nodes) along an assembly line or path. The manufacturing pallets typically include one or more control system components for controlling various actuators, motors, etc. for implementing an assembly step at a given station. Conventional systems provided for physical connection of various apparatus to the pallets at each assembly station, such as pressurized air for operating pneumatic actuators, electrical supply power, and cabling for connecting I/O and other control components located on the moving system to control system components located at the assembly station. This physical connection and subsequent disconnection, however, is time consuming and adds cost and complexity to the manufacturing operation. Recent developments include increased usage of electrical actuators to eliminate pneumatic components and associated physical interconnections, as well as the use of wireless communications equipment including commercially available technologies such as WiFi, WLan, etc. for exchanging data between control elements of the moving system and the assembly station.
The use of wireless communications apparatus for control data transfer thus reduces the need for physical interconnection of control cables at each station. However, many industrial manufacturing sites include many assembly stations or cells located in close proximity to one another, and the pallets are often separated by only short distances as they travel along the assembly path. In this common situation, therefore, wireless communications equipment of the stations and pallets receive signals from a number of different sources at any given time, whereby each wireless entity must be assigned a unique address and identity to avoid cross talk and confusion in the overall wireless network. With respect to industrial control systems, moreover, the moving pallets typically include one or more slave components that communicate with a master control component associated with the current assembly station. The control system communications protocols often mandate that each component be assigned a unique address for wireless communications such that the master locations know what control system components are valid for control information communication, and must know who they are communicating with at any given moment. Consequently, conventional attempts at utilizing wireless communications for data transfer between industrial control system components in assembly line situations using smart pallets with on-board control elements and stationary assembly cell control components require exhaustive address assignment and management, including reconfiguration of the stationary and moving control devices when a new pallet is introduced into the system or where the system is changed to perform a different function in the manufacturing process.